Usually, a communication terminal such as a mobile telephone or a PHS is provided with an antenna. If the communication terminal is placed on a metal plate of a steel desk, etc., with the communication terminal laid on its side, the antenna is brought close to the metal plate and thus interconnection occurs and a current of an opposite phase to the current flowing through the antenna flows into the metal face, changing the radiation directivity of the antenna and largely changing the impedance characteristic. Thus, the matching state comes undone and the antenna gain is degraded; this is a problem.
To solve this problem, a small radio described in JP-A-10-126304 (patent document 1) is provided with a whip antenna in the upper part of the rear and thus a rib for adjusting the reception sensitivity of the whip antenna is installed at a balanced position so that the upper side of the main body of the small radio floats when the main body of the small radio is laid on its side, as shown in FIG. 9. Accordingly, if the small radio is placed on a metal plate, the antenna gain is not degraded and good reception sensitivity can be realized.
As an alternative method, a technique of switching an antenna element and a matching circuit by a switching element for impedance matching on a metal plate or a technique of providing a subantenna for also radiating on a metal plate is available.
(Patent Document 1) JP-A-10-126304
However, in the technique of installing the rib at the rear of the small radio described above, the thickness of the main body increases as much as the rib thickness and thus the small radio cannot be slimmed and the rib gives a large impact from the aspect of the design and thus the outward shape is impaired; this is a problem. In the technique switching of an antenna element and a matching circuit by a switching element or the technique of providing a subantenna, the circuit configuration and control become complicated and the cost increases and in addition, the technique is also undesirable for miniaturization. Thus, a communication terminal for suppressing degradation of the antenna gain if the main body of the communication terminal is placed on a metal plate with the main body laid on its side without the need for changing the size, the design, etc., of the terminal is demanded.
The invention is embodied in view of the problems in the related art and the demand described above and it is an object of the invention to provide a communication terminal capable of keeping the reception sensitivity good if the communication terminal is placed on a metal plate with the communication terminal laid on its side without the need for changing the size or the design of the main body of the communication terminal.